Plasma processing apparatuses are often used in semiconductor manufacturing processes. A plasma processing apparatus supplies radio-frequency power to a plasma processing unit having a chamber in which a substrate to be processed is accommodated to generate plasma in the chamber, and performs a plasma processing such as, for example, an etching processing or a film forming processing by the plasma.
In such a plasma processing apparatus, an impedance matching device is provided between a radio-frequency power supply and a plasma processing unit in order to efficiently supply radio-frequency power from the radio-frequency power supply to the plasma processing unit during the processing. The impedance matching device automatically matches the impedance on the radio-frequency power supply side with the impedance on the load (e.g., an electrode, plasma, or chamber) side. Since the radio-frequency power supply and transmission cables are usually designed to have a pure resistance output of 50Ω, the matching circuit of the impedance matching device is adjusted such that the impedance on the load side in which the impedance matching device is also included is 50Ω.
The impedance matching device basically includes two variable elements (e.g., variable capacitors), and the load side impedance is capable of being adjusted by adjusting the position of the variable elements. Then, when the impedance of the plasma load changes due to, for example, pressure fluctuation during the plasma processing, the positions (reactance) of the variable elements are adjusted so as to automatically match the impedance on the load side to a matching point (50Ω).
As for the impedance matching device, for example, the impedance matching devices described in Japanese Patent Laid-Open Publication No. 10-209789 and International Publication Pamphlet No. WO 2017/002196 are generally used. In Japanese Patent Laid-Open Publication No. 10-209789 and International Publication Pamphlet No. WO 2017/002196, an impedance having two variable capacitors as a matching circuit is used. Then, the load side impedance is measured, and the positions of the two variable capacitors are alternately shifted such that the measured value approaches a target value (a matching point).